1. Field of the Invention
This invention relates to floating offshore platforms. More particularly, it relates to the water ballast and bilge systems used in floating offshore platforms.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Various floating structures are used for offshore drilling and production operations. Examples include tension leg platforms (TLP's), semi-submersible floating vessels (“semis”), spars and floating production, storage and offloading vessels (FPSO's). Each of these vessel types may include a water ballast system.
A ship may have a single ballast tank near its center or multiple ballast tanks typically on either side. A large vessel typically will have several ballast tanks including double bottom tanks, wing tanks as well as forepeak and aftpeak tanks. Adding ballast to a vessel lowers its center of gravity, and increases the draft of the vessel. Increased draft may be required for proper propeller immersion.
A ballast tank can be filled or emptied in order to adjust the amount of ballast force. Ships designed for carrying large amounts of cargo must take on ballast water for proper stability when travelling with light loads and discharge water when heavily laden with cargo. Small sailboats designed to be lightweight for being pulled behind automobiles on trailers can be designed with ballast tanks that may be emptied when the boat is removed from the water.
In submarines, ballast tanks are used to allow the vessel to submerge, water being taken in to alter the vessel's buoyancy and allow the submarine to dive. In order for the submarine to surface, water is displaced from the tanks using compressed air, and the vessel becomes positively buoyant again, allowing it to rise to the surface. A submarine may have several types of ballast tank: the main ballast tanks, which are the main tanks used for diving and surfacing, and trimming tanks, which are used to adjust the submarine's attitude (its ‘trim’) both on the surface and when underwater.
Ballast tanks are also integral to the stability and operation of deepwater offshore oil platforms and similar structures such as floating wind turbines. The ballast facilitates hydrodynamic stability by moving the center-of-mass as low as possible, placing it beneath the air-filled buoyancy tank(s).
Vessels such as TLP's, semis, spars and FPSO's typically require ballast tanks for weight and trim control. These tanks are usually distributed throughout the vessel, and a piping system allows these tanks to be filled and drained (ballasted). The piping system is typically located near the lower parts of each tank.